Ophthalmologic surgery often requires the use of a physiologic irrigation solution to protect and maintain the physiological integrity of intraocular tissues. Examples of ophthalmologic surgical procedures typically requiring irrigation solutions include cataract extraction and lens replacement and refractive lens exchange procedures, corneal transplant procedures and vitreoretinal operations and trabeculectomy procedures for glaucoma. Throughout the intraocular surgery, a patient's pupil must be sufficiently dilated to permit a clear operative field and to limit the trauma that can be associated with the procedure.
Pupil dilation (mydriasis) is typically achieved by dilating the eye preoperatively by topical administration of a mydriatic agent. Preoperatively applied mydriatic agents that may typically be administered include sympathomimetics, such as alpha-1 adrenergic receptor agonists, and anticholinergic agents, such as anti-muscarinics. Anticholinergic agents may be selected when longer action is desired, because they provide both cycloplegia (paralysis of the ciliary muscle) and mydriasis, e.g., tropicamide exhibits a half-life of approximately 4-6 hours. However, for many procedures, alpha-1 adrenergics will be preferred because they provide mydriasis but not cycloplegia. Alpha-1 adrenergics are thus shorter acting, causing mydriasis during a surgical procedure and allowing the pupil to return to its normal state shortly after completion of the procedure.
During the surgery, as the tips of surgical tools are inserted into the anterior chamber of the eye, the iris sphincter muscle tends to constrict (miosis), reducing the window defined by the pupil. If pupil diameter is not maintained adequately throughout the procedure, the risk of injuring structures within the eye increases and the required operating time is often prolonged. Clinically significant reductions in pupil diameter are associated with an increase in procedure-related complications, including posterior capsule tears, retained lens fragments and vitreous leaks.
Many ophthalmologic surgeons may incorporate epinephrine into the intraocular irrigation solution to assist in the maintenance of pupil dilation. Toxic anterior segment syndrome (TASS) is an acute, noninfectious inflammation of the anterior segment of the eye. TASS is a serious complication that can be associated with anterior segment eye surgery, most commonly cataract surgery. Various contaminants have been implicated as causes of TASS. The use of epinephrine including preservatives in intraocular irrigation solutions is one of a number of factors that has been associated with incidences of TASS after cataract surgery. See, e.g., http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5625a2.htm, accessed Jul. 9, 2012. Even “preservative-free” epinephrine, meaning epinephrine that does not include an antimicrobial agent, still includes sodium metabisulfite as an antioxidant, which has also been implicated by ophthalmologists as associated with potential toxicity to the corneal endothelium (Slack, et al., A bisulfite-free intraocular epinephrine solution, Am J Ophthalmol.; 110(1):77-82 (1990)).
Phenylephrine is another alpha-1 adrenergic agent that is sometimes administered topically prior to surgery to promote mydriasis, but is not approved in the United States in a preservative- and antioxidant-free form for single-use injection. Examples of approved phenylephrine HCL solutions include either 0.01% benzalkonium chloride (AK-DILATE™ from Akorn, available in 2 ml and 5 ml plastic dropper bottles; from Falcon Pharmaceuticals and Alcon Laboratories in multi-use 3 ml and 5 ml dropper bottles) and a “preservative-free” formulation that does not include an antimicrobial preservative but that still includes 2 mg of sodium metabisulfite as an antioxidant (Neo-Synephrine® from InterMed Medical Ltd., available in a spray bottle).
It is also desirable to reduce postoperative pain and irritation for patient comfort. Because of this, patients may be treated preoperatively or postoperatively with a nonsteroidal anti-inflammatory drug (NSAID). Although cataract surgery (for example) is typically not associated with a high degree of post-operative pain, there is a need to minimize the number of those patients in the minority who do experience more severe post-operative pain. This is significant both because such patients experience discomfort and may have concern that their procedure did not go well, and because patients may need to reexamined as a precaution to ensure that there is not a serious complication leading to the pain.
Various methods of delivery of ocular drugs, such as NSAIDs, are conventionally employed, each of which has limitations. These limitations may include corneal and conjuctival toxicity, tissue injury, globe perforation, optic nerve trauma, central retinal artery and/or vein occlusion, direct retinal drug toxicity, and systemic side effects. For example, topical medications applied drop-wise are frequently impeded in reaching a targeted ocular site due to the eye's natural protective surface. In many situations, a rather small percentage of the medication applied to the surface of the eye will actually reach the desired therapeutic site of action.
To achieve sufficient concentration of drug delivered to the back of the eye, drugs such as NSAIDs are frequently administered systemically at very high doses. These levels are necessary to overcome the blood-retina barrier that protects the back of the eye from selected drug molecules coming from the blood stream. For surgical procedures, injectable drug solutions are sometimes injected directly into the back of the eye. Subconjuctival and peribulbar periocular injections are used when higher local concentrations are needed and when drugs with poor penetration characteristics need to be delivered. Intracameral injections directly into the anterior chamber are used in cataract surgery.
Ketorolac is an NSAID that is commercially available in preserved form for ocular use. Acular® from Allergan is a ketorolac tromethamine solution that includes benzalkonium chloride 0.01% as a preservative, available in 3 ml and 6 ml dropper bottles. Bedford Laboratories also supplies ketorolac tromethamine in a concentrated form (15 mg or 30 mg in 1 mL or 60 mg or 300 mg in 10 mL) for injection for intravascular or intramuscular administration. Allergan supplies a preservative-free 0.45% ketorolac tromethamine ophthalmic solution, which is formulated with carboxymethylcellulose sodium, sodium chloride, sodium citrate dehydrate, in individual use vials under the tradename Acuvail®.
While intracameral injection provides a prompt method of achieving a concentration, it can be associated with corneal toxicity. However, this method suffers from the fact that these drugs are quickly removed by the eye's natural circulatory process. Thus, injectable solutions rapidly lose their therapeutic benefit, often necessitating frequent, large dose injections that can carry toxicity risks. Sustained release formulations, such as viscoelastic gels containing microcapsules, may be injected intraocularly for a longer duration of action. However, there may be some delay in reaching a local therapeutic concentration of drug. Hence, there exists a need for controlled methods of ocular delivery during ophthalmologic procedures.
Solutions that have been used in ophthalmologic surgical irrigation include normal saline, lactated Ringer's solution and Hartmann's lactated Ringer's solution, but these are not optimal due to potential unfavorable corneal and endothelial effects. Other aqueous solutions that include agents such as electrolytes, buffering agents for pH adjustment, glutathione and/or energy sources such as dextrose, better protect the tissues of the eye, but do not address other physiologic processes associated with surgery. One commonly used solution for ophthalmologic irrigation is a two part buffered electrolyte and glutathione solution disclosed in U.S. Pat. No. 4,550,022 to Garabedian et al., the disclosure of which is hereby expressly incorporated by reference. The two parts of this solution are mixed just prior to administration to ensure stability. These solutions are formulated with a goal of maintaining the health of ocular tissues during surgery.
Another example of a modified solution is disclosed in International PCT Application WO 94/08602 in the name of inventors Gan et al., the disclosure of which is hereby incorporated by reference. This application discloses the inclusion of a mydriatic agent, such as epinephrine, in ocular irrigation solutions. Still another example is provided by International PCT Application WO 95/16435 in the name of inventors Cagle et al., which discloses the inclusion of non-steroidal anti-inflammatory drugs (NSAIDs) in an ophthalmologic irrigation solution.